• Support PF! Buy your school textbooks, materials and every day products Here!

Wave Velocities

  • Thread starter tigger88
  • Start date
  • #1
21
0

Homework Statement



I'm just confused by notation in this question, because the textbook I use has different notation than my course notes and now I'm just not sure what anything means.

Homework Equations



Group velocity x Phase velocity = c^2

The Attempt at a Solution



What is c in this case? Is it the speed of light, or some other velocity?
I know it's a really stupid question...

Ta for any help though.
 

Answers and Replies

  • #2
79
0
Well, I assume that it is the speed of light. But really, the equation is not true in general.
Yes, photons move at c in free space, so phase velocity is c in free space (but inside midiums, the speed would get lower.).
However, the group velocity, could actually be lower than c. even 0. Just for reference, this is called EIT.
So if it is someother speed, well, normally it would be denoted as v, instead of c. c is normally reserved for the speed of light, or constant.
I guess what the most important part of this equation is that group velocity and phase velocity are the same in most of the cases: so if it is light, then it is c^2; if it is something else, then it is v^2. It is kinda open interpretation.
 
  • #3
diazona
Homework Helper
2,175
6
According to Wikipedia it is indeed the speed of light. I've never seen that particular equation before myself, but the derivation on Wikipedia looks reasonable...
 

Related Threads for: Wave Velocities

Replies
2
Views
1K
  • Last Post
Replies
2
Views
6K
  • Last Post
Replies
1
Views
815
  • Last Post
Replies
8
Views
2K
  • Last Post
Replies
0
Views
2K
  • Last Post
Replies
3
Views
2K
Replies
15
Views
10K
Replies
1
Views
1K
Top